Wireline logging is used to obtain a continuous record of petrophysical properties of a formation, such as, but not limited to, resistivity, anisotropy, dip angle of bed, radioactivity, density, porosity, acoustic properties, and pressure properties. In wireline logging, a logging tool is attached to a wireline and is lowered into a well borehole. The logging tool contains various sensor components used to obtain information relating to the formation's properties.
Electromagnetic induction logging is a technique that is sometimes used in wireline logging. In induction logging, electromagnetic induction tools are used to determine resistivity or conductivity of a formation surrounding a wellbore. Electromagnetic induction logging tools typically include at least one transmitting coil and at least one receiving coil. An alternating current having at least one frequency is conducted through the at least one transmitting coil. The alternating current induces eddy currents to flow within surrounding geological formations. The eddy current in turn induces voltages in the at least one receiving coil. The voltages induced in the at least one receiving coil are converted to apparent conductivities through a linear relationship that is based on an assumption that conductivity of the formation is insignificant. When the formation conductivity value is not insignificant, however, the voltages induced in the at least one receiver coil relate non-linearly to the formation conductivity. The difference between the derived linear relationship and the actual nonlinear formation conductivity is referred to as “skin effect.” The skin effect makes the apparent conductivity value smaller than its true value and causes non-linearity of the measured values. Transverse measurements at the borehole may also be strongly affected by distortions resulting from changes in the diameter of the borehole or by variances in the thickness of an invaded zone proximate the wellbore. Resistivity measurements may be less reliable due to the foregoing conditions.
The illustrated figures are only exemplary and are not intended to assert or imply any limitation with regard to the environment, architecture, design, or process in which different embodiments may be implemented.